Various hybrid powertrain architectures are known for managing the input and output torques of various prime-movers in hybrid vehicles, most commonly internal combustion engines and electric machines. One such hybrid powertrain architecture comprises a two-mode, compound-split, electro-mechanical transmission which utilizes an input member for receiving motive torque from a prime mover power source, typically an internal combustion engine, and an output member for delivering motive torque from the transmission to a driveline of the vehicle. First and second electrical machines are operatively connected to an electrical energy storage device for interchanging electrical power therebetween. The first and second electrical machines comprise motor/generators operable to transform the electrical power to motive torque for input to the transmission, independent of torque input from the internal combustion engine. The first and second electrical machines are operable to transform vehicle kinetic energy, transmitted through the vehicle driveline, to electrical energy potential that is storable in the electrical energy storage device. A control unit is provided for regulating the electrical power interchange between the electrical energy storage device and the first and second motor/generators.
Engineers implementing powertrain systems including transmissions are tasked with developing gear shifting schemes. Such transmission systems typically include devices able to operate in one of a plurality of fixed-gear modes, wherein shifting between gears occurs in response to predetermined operating conditions, and often not involving an overt request for shift from a vehicle operator.
An exemplary transmission includes a plurality of torque-transmitting clutches. When a shift change is commanded, torque must be off-loaded from a currently operating clutch associated with operation in a current gear and on-loaded to another clutch associated with operation in another gear.
An ongoing concern for designers of transmission devices is to develop torque-transmitting clutches that are sufficiently large enough to transmit required torque, able to manage temperatures, and meet durability targets, but meet constraints related to packaging envelope, size, and cost. Furthermore, engineers must be cognizant of thermal energy generated during clutch slippage, and effect of such thermal energy on transmission performance and durability.
Therefore, there is a need to for a method and apparatus to offload torque from a currently operating clutch associated with operation in a current gear to address concerns mentioned hereinabove.